The present invention relates to an ink-jet printer which prints an image onto a print medium held on a rotary drum with ink ejected from a print head, and particularly, to an ink-jet printer in which ink is supplied from an ink tank apart from the print head.
Conventionally, serial-type color ink-jet printers are widely spreading. In the serial-type ink-jet printer, a plurality of print heads and ink tanks of a relatively small capacity are integrally mounted on a carriage, and the carriage is movably attached to a guide bar extending across a paper sheet. The paper sheet is fed in a direction perpendicular to the guide bar at a constant pitch, and the carriage is moved along the guide bar each time the paper sheet is fed for one pitch. During the movement of the carriage, the print heads eject inks of different colors respectively supplied from the ink tanks In the structure as described above, for example, a color image of A4 size is printed out in ten minutes. Thus, the serial-type ink-jet printer operates at a slow print speed of 0.1 sheet per minute.
In recent years, a drum rotation type ink-jet printer capable of printing a color image at a higher speed has been suggested. This ink-jet printer includes a rotary drum rotating in one direction and a print head disposed to face a paper sheet held on the rotary drum. The print head has a plurality of nozzle units which are arranged along the peripheral surface of the rotary drum and eject inks of different colors onto the paper sheet rotating together with the rotary drum. Each nozzle unit has a plurality of ink-jet nozzles disposed across the paper sheet in the axial direction of the rotary drum. The color image is printed with inks ejected from nozzle units. In this structure, for example, a color image of A4 size can be printed out in about two or three seconds.
In this drum-rotation type ink-jet printer, a plurality of ink tanks are placed apart from the print head to store inks of different colors to be supplied to the nozzle units of the print head. Each ink tank is connected to a corresponding nozzle unit via a supply tube, and are filled with ink supplied from an ink reserve bottle detachably attached thereto. Ink is fed to an ink pressure chamber of the nozzle unit by a supply pump having a valve function and interposed in the supply tube. At the time of printing, the supply pump is stopped in a valve-open state, and the nozzle unit is driven to eject ink. Upon consumption of ink for ejection, an amount of ink consumed in the ink pressure chamber is supplemented through the supply tube by capillary phenomenon.
However, the drum-rotation type ink-jet printer has a problem that leakage of ink is caused by impacts and vibrations applied from a transporter vehicle or the like. The ink leakage occurs when the supply tube comes off from the ink tank or when the ink reserve bottle tilts with respect to the ink tank.